Is a Muslim considered an infidel if he misses the Fajr prayer after a deep sleep and does not wake up despite his father's attempts to awaken him by phone?

There is no sin upon you for what happened, as the pen is lifted from the sleeper and he is not held accountable for what occurs from him. You are only required to pray the prayer upon waking up. We advise you to abandon obsessive thoughts and to be diligent in sleeping early.