I bought Minecraft for my cell phone and computer, some time ago I can log on to my cell phone using my PC account.
(I hope you know what I mean)
Do you have Windows 10 Edition or the Java Edition on the PC? If you have Java it won't work because Java logs in with a Mojang account and Win10 (and Pocket) with a Microsoft account. You can't combine these. If you have Win10 Edition you can easily log in with a Microsoft account as well as with the mobile phone. If you have Java Edition you can do the same with username, password and email then you can enter the same and you only have to enter password & co. Notice.