So is it, "Are you there, Mom?" or "Are you there, mom?" This is an error I see writers making all the time, but it's an easy one to spot and fix if you know the rules.
Think of family titles – mom, dad, mother, grandpa, and so on – as alternative names. Any place where you would naturally use someone's name, you should capitalize the family title. Any place where you would use a pronoun, the title should be lowercase.
For example, "Would you pass me the sriracha, Barbara?" If Barbara is your mom, this sentence would be "Would you pass me the sriracha, Mom?" If Barbara is your friend Amy's mom, and you can't get her attention despite jumping up and waving your arms, you could say to Amy, "Hey, would you ask your mom to pass the sriracha?"