I say, and with God's success: If the call to prayer on the phone is correct, meaning the timing is in accordance with the timing of the country where the call is made, it can be relied upon, and it is permissible to break the fast and pray based on it. However, if it is incorrect and you relied on it as in the situation you mentioned, then you have broken your fast by mistake and you must make up for it. And God knows best.