I think my mom (84) has forgotten how to use the telephone. Advice?

I thinks she's making excuses for not using one. She used to call me just about all the time, whenever I was at work or out of the house for a while. I haven't received calls from her for months. I thought that she just decided to stop calling me because she didn't want to bother me. I asked my relatives if they've had any calls from her lately, and some haven't heard from her in a long time, either. Yesterday, just to test this, I told her I wasn't sure my cell phone was working properly, and I asked her to call my number to see if it rings. I keep my number written in large text/numbers right near the phone. I was shocked to have to tell her where the phone was first! After that was done, I asked her to start dialing. She hit the first number right away, but then she lost her attention span or something, and even though I ended up telling her what numbers to dial, it had taken too long. The operator said, "if you'd like to make a call......." She hung up and said there's something wrong with my phone. I forgot to mention that she has dementia. I'm going to have her checked for a UTI tomorrow, but if it comes back negative and she still has this problem, that scares me to death. She also has a Lifeline button, but she doesn't want to wear it, and sometimes I wonder if she knows what its for, too. As a matter of fact, I asked her if she wanted to put her hearing aids on today, and she looked at them and asked me what they were. When I told her, she said, " I'll save them and use them for when I feel sick." Well, now I feel sick. She usually stays home at night when I work, and then I spend my days and evenings with her. I can still call her and she usually answers, but.......*sigh.*