How do I stop being on call for every small change to Mum's phone?

Mum sent three screenshots while I was at work: “Which one do I press?” The first was about changing the font size. By the third, she had opened a menu I did not recognise either.

I helped her set up the phone last month. Since then, even small questions arrive with “Can you just have a look?” I usually reply quickly because it feels kinder than leaving her unsure. Yesterday I left a meal with friends to talk her through something that could have waited.

She uses the phone confidently for her shop orders and chatting with family. This is not a case of her being unable to use it. She would simply rather ask me than search through help pages, and I have made that option very easy.

I want to offer a regular time for ordinary questions and ask her to state what is actually urgent. I am worried she will hear that as me withdrawing a favour after encouraging her to get the phone.

How would you change this arrangement kindly? I still want to help. I also want a font-size question to stay a font-size question when I am eating dinner.