Sure you can do it but why? CCTV is dirt cheap these days. Id rather go with a pro setup that has a high quality image that can be bolted professionally into the wall. Using a camera would require faffing and fiddling around to get it working then making sure it's constantly powered up as well as mounted. Seems like more effort right?

 

Storage would be a problem, and the battery will wear out very quickly if it's in, unless it can be powered without one. I wouldn't do it, there's very cheap options available, and as for the phone, there are plenty of other uses for it.

 

I bought an old blocked S4 mini about 3 years ago for £10, installed Alfred camera on it and on my iPhone and Shield TV and set it up in position keeping it plugged in to power while turning off the screen.

It’s been super useful for monitoring garden/pets and stuff, I could imagine better models being better resolution, but it’s definitely a useful way to recycle old useless phones, as you can hook up as many as you want.