Hello J.brow,
Thank you for posting in the Apple Support Communities. I understand you've been unable to sign into an Apple ID on an iPhone.
Have you been able to sign in since you made this post? If not, I have a few steps that may help.
Is the iPhone in question responsive, or does it appear to be frozen? If it's still responding, Restart your iPhone, iPad, or iPod touch and see if this helps. On the other hand, if it's unresponsive entirely, you may need to force restart. The steps will vary by device, and you'll find them in the "If your screen is black or frozen" section of this link: If your iPhone, iPad, or iPod touch won't turn on or is frozen.
Once you restart, give it a try. If the issue persists, I recommend making sure that you've tried signing in using a Wi-Fi connection, and a cellular connection. If you find one of these works, it should enable you sign in successfully.
I hope this helps.
Take care.