Well, it shouldn't be a problem. Let meh explain. If you have 2 pc's on one wifi network they will have the same EXTERNAL ip address. Now you are using Tails which means that ip on one of your devices will be masked. You could unmask it by logging in a website that you previously logged in with your phone using your real ip. If the ISP and the website is tracking you and you connect with both your pc and phone at the same time on the same website they could POSSIBLY find out your real ip. Or at least it would be easier for them if Tor doesn't change the circuit each 10 minutes. So all in all i don't think you should be really thinking about this to much. "Tor guys" pretty much took care about this xD.