What is the ruling on helping one's mother charge her phone or giving her money, when it is highly probable that she will use it to disobey Allah?

It is a principle of Islamic law that aiding in sin is itself a sin. Therefore, if you are certain that your mother will spend the money or use the phone in a sinful way, then do not assist her in that. However, if it is merely a doubt, then the default is the obligation to obey and honor her.