Dua to be recited when leaving a gathering

I have learnt the dua' said at the end of a gathering ("subhanakallahumma wa bihamdika ashhadu...") which compensates for vain talk etc in the gathering. My question is, can this dua also be said in the end of a telephone conversation? Since often much vain talk and possible backbiting etc goes on in telephone conversations. If so, is it OK if I say the dua after having closed the phone at the end of the conversation (rather than saying it whilst still in conversation) in order to not appear weird/strange (since the person I speak with might not understand)?