Blink, Ring, Wyze, and probably others make wireless cameras. Depending on which one you get they can be powered by Energizer Lithium AAs, rechargeable battery packs, or plugged into AC.
The only thing you need for your phone is to download their app and (assuming you want to save clips to the cloud) select a monthly plan. You can forego the monthly plan if you do not need the ability to save clips to the cloud.
I have Blink cameras, and they work well. Their Sync Module that the cameras connect to plugs in somewhere in the house, and you can insert a memory card that will save the clips locally rather than to the cloud.
Of course there are also wireless trail cams.