Hi Mohammed,
If there are no plans to increase the number of users later on then you can go with 2911 as it supports a max of 50 IP phones. However, if there are any plans for expansion then you can go for BE6000S.
BE6000S Model: Cisco Unified Communications on Cisco UCS E160D M2 on Cisco Integrated Services Router (ISR) 2921V with integrated gateway supports up to 150 users, 300 devices, and point-to-point video calls.
You can read more about it in the datasheets.
HTH
Manish