Moved to 5th Generation forum.
Assumptions: That the unspecified Pioneer head unit actually has a USB connection at the rear. Most do, but not all. Also that the Factory USB wiring has a USB plug at the other end. My Pajero does but my Triton had no USB at all. Options 3 or 4 may be your only choices.
1. Take back to installer and get them to plug the USB in to the head unit.
2. Remove head unit and plug in USB yourself.
3. Buy a cigarette lighter USB charging adaptor and use that to charge your phone.
4. Charge your phone each night instead.
If work is so terrific, why do they have to pay us to do it?