Need cartridge advice for Philips turntable

I'm not sure why Grado would say that. It looks like it has a standard 1/2" mount. They may have been thinking of a different turntable. Check your current cartridge. Measure the distance between the mounting holes. Should be 1/2". If so you can use just about any modern cartridge.
The Grado Prestige Blue would fit the bill perfectly and allow you to upgrade the stylus in the future.

I set up  a Philips GA 312, or maybe 212, for a friend several years ago.It is a very good basic table.Go to vinylengine.com for a manual, and other info.Go to turntablebasics.com to look at their inexpensive cartridges. Also check for a belt, alignment gauge, stylus force gauge, dust brush, etc.They show a lot of helpful basic info on their site with pics of 1/2" and P-mounts.

A Grado cart will definitely fit; no question about that. I assumed the Grado cart was "not compatible" due to a compliance issue.

...or maybe a hum issue. Grado Service didn't elaborate on why it was not compatible.

The 312 has a low mass arm which requires a high compliance cartridge.

I had 2 of them in the late 70's for a few weeks (long story) and one came with a Philips branded cartridge and the other with an Audio Technica (sp)? cartridge.

The Philips (whatever it was) sounded sounded pretty good and the AT not so much (kind of bright/thin).

Anyway, I replaced I replaced the AT with a Sure V15 MkIII and was surprised/pleased with how good the combo sounded compared to my various Thorens/SME/Sure V15 MkIII decks.


I also briefly had the 212 version in 1974-75, or so, but is was so affected by footfalls (100+ year old house) I returned it for a store credit.

So...

High compliance, which would rule out the Grado I currently use.

DeKay

Just Googled the old Philips cartridge I mentioned above and they and their replacement styli are readily available on the used/NOS market.

You would want to go with a 401 (or higher) and not the 400/conical version.

There is also a new Philips 501-II listed @ Thakker for $120/US, but I didn't see any spec's listed.

https://www.thakker.eu/en/pickup/philips-gp-501-mkii-cartridge/a-5160?currency=USD

My decks came with a plastic cartridge alignment guide (fitted over the head shell) that actually worked.

DeKay

The Grado Prestige Blue is a high compliance cartridge at 20 um/mN and will do just fine in that arm.

You could find Philips MM cartridges