Phono stage or pre Amp? which is most important.

The phono stage is the most important piece of line level electronics as it has to deal with a very low input voltage. Signal to noise ratio becomes more critical as accuracy of the RIAA reversal. In the context of the system you have the Project should be fine. If you decide you really like vinyl then I would upgrade the cartridge and phono stage at the same time. I am unfamiliar with the Naim. I like tube phono stages like Audio Research.  

I used that same Linn table/arm combo for years and never considered it "cheap". Don’t be the guy that "knows the cost of everything and the value of nothing". Regarding your question, a budget phono-pre can sound excellent so I'd go big on the main preamp for now and get a better phono-pre later.

As an ex-Naim person, the biggest improvement you can make to a Naim system is to upgrade the power supplies if possible.  I had a 202, but I don't recall if you can use a hi-cap with it.  If you can, pick one up and your whole system would be elevated.  IMO, the phono preamp is fine with your cartridge.  

You can power a Stageline from the 202 and the 202 with the 200 or a hicap or you can power a stageline directly with a hicap. I suspect a stageline N would suit an AT95 rather well being a bit on the dark side.

They're all important but Mike is right, the phono stage is sort of a first among equals. Relative to what you have the table, arm and cart are good enough that you would probably be shocked to hear how much better they are through a good phono stage.  

As far as preamps go, any time and every time value and budget comes up the answer is a good tube integrated amp. You will get far more sound quality for your money than with separates. That is the most budget friendly step up. 

Finally, most important of all is what you want from your system. I know what I want, and so I know tubes and turntables are the way to go. I know to strongly consider Benz and Koetsu while never wasting a moments thought on AT, Lyra, etc I just don't want hyper I want music. But if you want your table to sound like digital then solid state and Naim with AT will get you a lot closer than tubes and Benz. Whatever it is, know that about yourself and be realistic is the winning combination.

Last time I heard a budget Pro-Ject phono stage, I thought it was pretty bad. In fact I think the model you have is even lower than what I heard (though it was several years ago). I’d suspect even that budget AT cartridge can do much better; that current phono stage is quite possibly the weak link. Try a Hagerman Bugle 3, it’s really affordable at $185 and sounds good! That leaves money to upgrade other stuff in the meantime. Then later, you can go for a big cart & phono stage upgrade together, when you're ready.

I would think nicer thoughts about your equipment,

The only thing 'cheap' (simply inexpensive) is the cartridge, I would suggest keeping it for a spare and getting a better one now or soon.

Stylus shape is important, definite audible differences, have a read:

https://sound-smith.com/articles/stylus-shape-information

Fineline, Microline, SAS, Shibata, all cost more, however they last longer, so look at cost per hour when comparing.

This one would be a terrific choice IMO

https://www.audio-technica.com/en-us/vm750sh

IF/AFTER you get further into Vinyl, then think about 
...........................................

Let's talk about proper cartridge mounting and precise alignments.

A few tools are needed, and some acquired skills are needed.

What are your skills?

AT 95 is a nice performer and your tt combo will benefit from a better phono stage. Start there and practice your alignment skills with this cartridge. 
G

My experience tells $500 phono pre and $1000 preamp will be a better choice than $250 phono pre and $2000 preamp.
The difference between $500 and $250 phono pre will be considerably bigger than the diff between $1000 and $2000 preamp.

In terms of partst:
$150 phono stage and $500 phono stage can be absolutely the same, but with different label and different box. Price is nothing in this case (in this category at least) and can’t be a guide. 

The Parasound Z-phono is a real killer in the lower price level. Also there are some vintage preamps that are known for having an exceptional phono stage. One of them is the Adcom GFP 565. Quite a performer at it's price point but with no digital inputs if that's an issue.

I think both.  If the preamp is not resolving enough, the resolution of the phono stage will not make its way through.  I upgraded a few years ago from a AyreK5xe MP Preamp to a Jeff Rowland Criterion and the sonic improvement was staggering.  I just upgraded my phono stage from an Asthetix Rhea to an Allnic H3000 and, once again, the improvement is staggering.  I wouldn't hear the improvement that I do from the Allnic through the Ayre.  

My Croft pre-amp is excellent and has an excellent phono stage built in .
Mr, Croft makes every one himself and everything is all hard wired and 5 12AX tubed .
2300 $ . I’ve only seen 1 on here in years . 2 years on here I got
a mint 2 year old trade-in from a dealer for $1400.He wanted 1700$.

Best pre out of the forty or so ones I’ve had in 40 years.
Only one close was the Eastern Electric Avant .

Thelad, do you think you may upgrade the table sometime in the future? If so a quality phono would make sense. 
If not perhaps a better cart would be in order first.

Elliottbnewcombjr's comments are well worth following.

what is more important, your brain or your heart?

$150 phono stage and $500 phono stage can be absolutely the same, but with different label and different box. Price is nothing in this case (in this category at least) and can’t be a guide.

I agree. There is always an exception. Same thing applies to any audio gears. There is always a giant killer.
But from my limited experience, I have not had $150 phono stage that sounds as good as $500 phono stage. I'd appreciate it if you recommend me a few. I am in need of at least one more phono preamp and I don't want to spend more than a couple of hundred dollars. My current phono stages are Yaqin MS12B, MAGI Phonomenal, and Phono stage in Plinius M16P preamp. $150 phono stage that sounds close to Yaqin would be nice.

I don't know if anyone's mentioned it but the Schiit Mani is a great deal for $130.. or were you looking for something with some "wow" factor?