Bearded dragons are not able to cough (they don't a chest diaphragm), he is actually sicking up hairs he has eaten, and if there are that many, it's very important to work out where he's finding them and how he's been able to ingest them .
Hairs can accumulate in the GIT and cause a very serious blockage and also impactions , I STRONGLY SUGGEST you ask a REPTILE / HERP VET to examine him and take xrays and ultrasound of his GIT to determine the extent of the problem and a treatment plan - surgery may be necessary to remove the accumulation of hairs.
This is a serious issue so I wouldn't wait to see the vet.
