My phone will reboot randomly and according to apollo logicboards bad

Have not had this phone for a terribly long time, and I bought it new. The phone would just randomly restart and it got so bad that I ended up taking it to Apollo to see if they could fix it. They got it to a screen that tell me to go to support.apple.com/iphone/restore and has the iTunes logo and a charger picture on the screen. They also told me that the logic board is most like the problem and that I would have to send it off to Apple to replace it for a good $300. They also told me that I could try restoring it and what not but they said that it most likely will not work. I have tryed restoring it but it has done nothing. Also have attempted to look for iPhone 7 logic boards but all I can find are the bare ones and I don't have a micro solder. Just wondering if anyone else can think of something else to try or if anyone else knows where I can find a logic board for my phone. I have already went and bought a new one but would like to have this one as a backup or might sell it to a friend. Also the screen has been cracked but it was cracked before this started happening.