even if 7841 Cisco Data S. says 7841 is compaltible for
What is the actual problem you are facing with these phones ?
By the way, if you are not seeing the device type (7841) while adding it to cucm, then plz install latest device pack in cucm.
There is for 9.1(x), if you're running 9.0(x), you won't find one, and you need to upgrade to a compatible release.
You can find the latest device pack for 9.1.2 at below link.