Looking for advice

I’m looking for advice from parents who have dealt with this.
My 7-year-old son is currently with his dad for summer parenting time. Before he left, I bought him his own phone because there have been ongoing issues with me being able to communicate with him during extended visits. My only goal was for him to have a way to talk to both sides of his family while he was away.
Despite repeatedly asking, I went four days without being allowed to speak to my son. I continued requesting phone calls, and they were either ignored or I was told he was busy.
There has also been a history of conflict. My son’s therapist has documented that his father has called me names in front of our son, which is concerning because I don’t want him caught in the middle of adult issues.
Our Tennessee Parenting Plan states:
“The right to unimpeded telephone conversations with the child at least twice a week at reasonable times and for reasonable durations. The parent exercising parenting time shall furnish the other parent with a telephone number where the child may be reached at the days and time specified in a parenting plan or other court order or, where days and times are not specified, at reasonable times.”
I’m keeping records of my requests to speak with him and the responses (or lack of response), but I’m wondering:
Has anyone dealt with a co-parent repeatedly refusing phone contact despite similar parenting plan language?
Did the court consider it a violation?
What helped resolve it?
My goal isn’t to interfere with his dad’s parenting time. I simply want my son to know he can maintain a healthy relationship with both parents while he’s away.