Hello Mario3,
you would need at least 13W *48 for the phones and you need also to provide power to make the switch to stay alive and function correctly.
13W*48 = 620 W you would need this power avaiable for POE
if you power supply is only 715W I am afraid you will not be able to put a phone on each port.
I think you would need a 900W power supply as minimum.
To support also more demanding POE devices 1100W power supplies are used.
see the datasheet
https://www.cisco.com/c/en/us/products/collateral/switches/catalyst-3850-series-switches/datasheet_c78-720918.html
for 48 ports POE+ or UPOE you need a 1100 W PS with 800 W available for POE.
Also what happens in your stack if one power supply fails ?
you should deploy redundant power supplies on each switch
Dual redundant modular power supplies
The Cisco Catalyst 3850 Series Switches support dual redundant power supplies.[6] The switch ships with one power supply by default, and the second power supply can be purchased at the time of ordering the switch or at a later time. If only one power supply is installed, it should always be in power supply bay 1. The switch also ships with three field-replaceable fans
or you should use 1100W PS and stack power cables
>>>Cisco StackPower® technology provides power stacking among stack members for power redundancy
Hope to help
Giuseppe
