You are seriously over thinking it. Especially since overload is much less likely than having too much. Your typical phono stage with 45 to 65 dB gain will output a normal 3 or so, right in the sweet spot of your preamp input range.
The volume range on virtually all preamps is so wide it just isn't a problem. Almost always, the worst that will happen is you have to turn the knob a lot more, or a lot less, than with your line level sources. This is where you stop and remind yourself, the position of the volume knob means nothing. It is nice if all the sources are at about the same level, because then you don't have to fiddle around as much. But that is pure convenience and nothing to do with sound quality. Do it a time or two, you will see.