Do you mean here in reference to meetings? Or to actual calls?
If you are referring to meetings/conference calls, use the meeting options and change the 'bypass the lobby' settings of the meeting to 'only you'. See article herehttps://support.microsoft.com/en-gb/office/change-participant-settings-for-a-teams-meeting-53261366-...
This means that everyone, including everyone else in your organisation or whoever you invited into the meeting will wait in the lobby and so no one can start the meeting until you are ready and let everyone in
If you want to make it that all meetings you schedule have 'only you' bypassing the lobby so people can only join meetings when you want them to, you should be able to set this in the Teams Admin Centre under meeting policies. It has been a recent add in the last few months
If you are referring to calls themselves then I raised a uservoice for this several months backhttps://microsoftteams.uservoice.com/forums/555103-public/suggestions/40553593-ability-to-turn-off-c...
Vote on it to push up the agenda and you'll be notified if it gets picked up
Hope this answers your question