Student pilot reported while making a visual approach the tower controller gave the instruction to go-around; then changed to side step left then go-around; in an urgent tone. Later the student learned a pilot; who had lost communication; had been cleared to land via mobile phone.

Narrative

I was doing a student solo XC. On my last leg of my XC I departed ZZZ1 from Runway A with a left turn out to the north and climbed to 2;500. I made my radio call to tower at ZZZ a short while later; I believe the ATIS information that I had coming in was information 1; and told them I was coming in for a full stop. ATC gave me a straight in approach and clearance to land on Runway B. While I was on final with my altitude approximately 1;000 feet AGL; at this point I received an urgent call from ATC telling me to go-around and then immediately was told not to go-around but to side step left then go-around to which I complied and maneuvered left and initiated my go around to get back into the traffic pattern. Upon getting back to my school I found out that while I was on final there was another aircraft (Cessna 172) that was not answering ATC calls or directions; that air craft had come into ZZZ and made right traffic and made a right base then final for Runway X at the same time that I was on final and the aircraft had converged from behind me and over me and according to ADS-B data he was within 30 feet directly over the top of me; at no point did the pilot of the other aircraft make any radio calls. I called Tower on the phone after I found out what had happened and spoke with Person A because I wanted to file a complaint on that pilot for his unsafe pilotage. A short while later I received a phone call from Person B at the tower and he said that the pilot of the Cessna had apparently lost his communications and made a phone call to them from his cell phone prior to entering Delta airspace and he was given clearance to make right traffic and cleared ahead of time for Runway B.