Yes, you need to use Jabber
If you want phone only mode, you only need CUCM and if you don't have LDAP, you can use UDS.
Your version is already out of support, CUCM 9.1 is EOS/EOL and is going out of support this year.
Reach out to your SE or the partner that you work with, to plan for the upgrade and see what options you have based on your support contracts and upgrade options.
HTH
java
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