Is it permissible for the one who is observing i’tikaaf to use the phone in order to help the Muslims?

Yes, it is permissible for the one who is observing i’tikaaf to use the phone to help the Muslims, if it is in he mosque where he is observing i’tikaaf, because he has not gone out of the mosque, But if it is outside the mosque then he should not go out for that. If he is a man who is needed to help the Muslims, he should not observe i’tikaaf, because helping the Muslims is more important than i’tikaaf, because helping others is benefiting both parties and good actions from which others also benefit are better than actions from which only the doer benefits, except in the case of actions that are regarded as requirements and obligations of Islam. 

End quote. 

Shaykh Muhammad ibn ‘Uthaymeen (may Allaah have mercy on him)