All IP-phones need to be supplied with power to operate.
Sangoma P series IP phones provide you with 2 options.
Using built in Power over Ethernet (PoE) option
Using the optional AC power adaptor
The PoE option is favored because it greatly simplifies deployment when using with PoE enabled switches. But if this option is not available to you, you can purchase PSUs and other phone accessories separately from the Sangoma store at https://portal.sangoma.com or from Sangoma partners.
Note that Sangoma P-series phones do not ship with power adaptors. These must be purchased separately if you are not planning on using the PoE method.