You can ask her if she does have any reviews anywhere, and if so, go and read those.

If not, then don't bother unless you are the real adventurous type.

nobody knows what to expect from someone unreviewed (or specifically recommended). Wait until your hobby radar gets better fine-tuned before you TOFFT.

If I see a escort I like in Backpage or similar but no reviews that explain if the escort offers full service or not--what should I ask her on the phone reguarding that? Alot of the women say they wont discuss it on the phone others say yes--Im not sure what is proper etiquette.

You shouldn't ask her anything.  If you don't know what to do in this situation, you should skip those ladies completely and find one that does have reviews.  Remember, if you can't trust her ad, you can't trust her to be honest.

If she doesn't have any reviews, you also don't know if she's the woman whose picture you like. If her BP pics look hot, but she doesn't have reviews, there's a good chance those pics are stolen. So wouldn't that make the question of whether she's full service sort of beside the point?

And the other thing you don't know is if she's LE.

No, the bad news is, if she's LE you WILL get FS !  But it won't be the kind of FS you were seeking!
Can you spell "full body cavity search?"

Don't discuss specifics on the phone - it is bad form and likely to get you disconnected.

Stick with well reviewed ladies.  A suggestion if you are interested in someone on BP, do a cross check on TER.  It will save you a lot of frustration.

Happy hunting.