In addition to judge's questions - how long are the children with Dad? How frequently does Mom entertain calls to Dad on her time? How long are these calls?
Frankly, even daily calls during Dad's (presumably) limited time seem excessive, with a few exceptions.
- the child is requesting to make the call every day
- the visit is for an extended period of time
Honestly, daily calls - never mind multiple calls per day - can be disruptive, regardless which home the kids are at. At the custodial parent's, there is homework, extracurriculars, family time, etc. At the noncustodial's - often much of the same. Plus, most NCPs get significantly less time, so incessant calls are that much more disruptive.
When my ex & I split, it wasn't amicable, so we had it written into the order that there was to be a call once a week - with the day/time specified by the parent w/o the kids - and the children were to be allowed to call at will. If we weren't home on that day/time, I would let my ex know where he could reach the kids (pre-cell days), let him know what time they'd be home for him to call there (and then make sure they were), or offer the option of calling the next day (or another better suited to him if there was a conflict). It mostly worked out. If the kids were with Dad for the w/e? I didn't call. If for their summer time? We followed the scheduled time.