You’d have to inspect them to be sure all the wires are terminated, and whether they used 568A or 568B wiring. Phone systems often follow 568A wiring while ethernet almost always uses 568B.
Either standard is just fine, as long as you use the same one on both ends. Otherwise you wind up with crossover cables built into your walls, and while most switches and nics figure this out all on their own, it can be hard to troubleshoot if you find one that doesn’t.
If you pull one of the faceplates off and take close up pics of where the wires go into the jacks, we can tell you which standard and whether they are wired right.
Then, you will need a punchdown tool for 110 blocks, a patch panel (or SMBs and more jacks) and some YouTube time to learn how to terminate jacks and patch panels. I teach people how do do this in about 10-20 minutes, so it’s not terribly complicated.
Just remember these things:
Keep as much twist in the wires as you can. It’s OK to ADD a twist if your wires don’t line up, but resist the urge to untwist unless you can get the next twist really close to the termination point.
Try to keep the sheath as tight as you can to the termination point. This can be hard to master, and your first terminations will likely be somewhat “leggy” as you learn.
The jacks and patch panels are designed to be terminated only once; each time you reterminate, the connection will get a little weaker. In practice, you can reterminate a jack or patch panel many times before you run into issues, so keep that in mind if you choose to reterminate a jack because it wasn’t quite right. So buy some extra jacks.