Will LEO track down former clients of providers through cell phone numbers?  I know I am over thinking this.  Had a poor experience, got out without a problem but now worried.

.....local LEO's do not have the funds, and manpower.  

I would not worry too much about the FEDS either, after all pros is small potatoes, and not really worth the money, time, and effort for them.  The FEDS will leave it to the locals, and as BWB said, the locals don't have the time, money or manpower to research cell phones.  They will post an ad, get a room, and do a sting in a motel before they will bother searching phone records.  More cost effective.

Just having your number in her phone does not prove anything.  In most jurisdictions, prostitution is a misdemeanor.  There is no incentive to waste a bunch of resources on a impossible to prove misdemeanor.  On rare occasion a client will get a phone call  (better to use a hobby phone!) from LE, a pimp or a scammer...  If it's not linked to you, it's untraceable.

If LE has traced your phone, they'll not be calling you...  they'll be confronting you!   Gee, I don't know who this is but wouldn't you tell me so I can charge you with something?  Yeah, right.  I don't even turn my hobby phone on, except when I'm actively using it.  If I ever thought it was compromised, in the next 20 seconds, it would be under the tires of my truck & then thrown away.  
So your hobby phone in a provider's phone means nothing.