Can I call my doctor on her cellphone? She has kids.

If she/he is ok. Confirm with your doctor. I allow my patients to call me.
Is this my mom? It's the only person I can think of that would ask this question.
Maybe. Most docs use an answering service to direct calls to the appropriate doc during or after hours. (most share on call responsibilities with others to maintain their family life) Some more independent docs give out their phone number to specific patients with special needs. A few do so for all. You must check with the office to see how this is handled. Most newer docs do neither.