Not clear what you're trying to accomplish.
Do you wish to replace a wall-wart phone charger with a big honkin'
ATX power supply? If so, be aware that, while the power supply standard
suggests that you can get a stable 5V output with no other load,
there's a lot of non-standard stuff goin' on in the highly competitive
PC market. Saving a dime on the design and have it still work in its
target PC is small comfort if the thing misbehaves in YOUR application.
Or if the technician copying the copy of a design screwed it up.
Why would you risk an expensive phone on a clunky solution?
Risk may be low, but the consequences might be devastating to the phone.
Wall-Warts are dirt cheap.
And chargers are not all dumb. I've got phones that complain
if you plug in a charger it doesn't recognize.