Why is the call button greyed out.

Thank you for your question. I think a possible answer to this could be that perhaps your calling permissions on Teams have been changed. If you are using Teams software in a corporate capacity that is subject to company oversight, then administrators may have restricted your access by amending the Teams Calling Policy. Hope this helps!

Another thing I’d check is whether the greyed-out button is specific to that particular colleague rather than the whole calling feature. If other coworkers can still be called normally, comparing the affected user’s account and Teams presence with a working colleague could narrow it down quickly. The exact error message and whether the button is greyed out in both desktop and web Teams would also be useful clues.

The header colour alone does not explain why calling is unavailable, and your screenshot does not establish whether this affects one conversation or every call. Start a new one-to-one chat with the colleague's correct work account, then try another internal colleague. Repeat the test in Teams on the web using the same account. If calling fails for everyone in both clients, ask your administrator to check your assigned Teams calling policy, particularly Make private calls, and the tenant's service health. Microsoft documents that this policy can prevent users from starting private calls or escalating chats to calls. If only this colleague is affected, compare both users' ability to call others and confirm whether either identity is external. Ordinary Teams-to-Teams calls should not be confused with telephone-network calling requirements. Give your administrator the exact error, failure time, client version, and those test results before changing policies.