All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The divorce delivered by your husband on phone or written in a paper is valid provided the husband himself acknowledges it or two reliable witnesses confirm that he has divorced you. In such case, you may marry any man you like after the completion of your ‘Iddah (legal waiting period for the divorced woman before she could marry again). If a wife does not have any proof for her divorce except her own claim that her husband has divorced her, in this case proceeding according to her claim is not permissible. So, she has to refer to the Islamic court to have her case settled according to the Sharee’ah.
Allah knows best.