who actually flies into Rhodes (from the UK)
Just to take Gatwick (because I have it to hand) last summer, it was
Britannia - Wed and Sat
First Choice - Wed (two flights) and Sat
Monarch - Wed (four flights) and Sat
MyTravel - Wed
Thomas Cook - Wed (two flights)
Excel - Wed, and Sat (three flights)
Gatwick total 11 flights on Wednesdays and 6 on Saturdays
Manchester will have been pretty much the same, with lesser numbers from other UK points. I would (guessing absolutely now) say 50 flights a week. As they are charters it is of course dependent on which airlines have secured contracts with which tour companies, these tend to change slightly from year to year.
The flights tend to run on the same days as tour companies find it convenient to have accommodation "changeover days" fixed, to give them the flexibility to perm flight origins and accommodation as required, and to give them the flexibility to merge flights easily in the shoulder season. Other destinations take other days to keep the aircraft utilised all week.