Hi there, my mother who is in overseas started to have delusion & phobia but most of the time she talks normal. how to convince her to visit doctor?

Hard to tell: You would be in a better position to know how your mother responds to advice. If you have already discussed this with her and she still refuses, using a pretext for evaluation with a doctor for other medical condition may be one way to approach it (you will need to bring this to the doctor's attention prior to the visit). There is no question that your mother badly needs professional help.