Quarantine is one of the harder stretches an inmate can go through, and the communication blackout on your end is genuinely stressful when nobody will tell you anything.
Here is what the inside of a quarantine period actually looks like. Inmates are locked down 24 hours a day with very limited exceptions. Three hours of rec yard time per week and three showers per week are the standard allowances. Outside of those windows, they are in the cell.
Phone access during quarantine is severely restricted but not completely cut off. The typical allowance is one 15-minute call per seven days. Over a 21-day quarantine, that works out to three calls total. The timing of those calls depends on when staff facilitates them, which is not always predictable, so missed connections during that window can mean waiting another full week for the next opportunity.
If he has not been able to reach you yet, it likely means the call window either has not come up yet or the timing did not line up. It is not a sign that something is wrong.
The best thing you can do right now is send a letter through InmateAid, so something is waiting for him. Mail still moves during quarantine and having a letter arrive means he knows you are there and thinking about him even when the calls are not coming through. Keep it upbeat, let him know you understand what is happening, and give him something to hold onto until he can reach you.