Having a quick look through the Field Manuals, using an average of 60 Clusters for the three big Clans plus the Blood Spirits and using their FM strength for the rest provides a total of over 650 Clusters*. That figure does not include the Burrocks, but going on what we know from the Absorbtion War a guess of about 30-40 Clusters for them seems pretty reasonable, which would put the total in excess of 680, maybe into the 690s.
This is also pretty significant since the Clans actually lost strength in the post-Revival period when things hotted up in the Homeworlds. I could be a bit more specific about numbers if I combed through the Field Manuals, but my eyes are starting to bug out with all the facts and figures I've analysed here recently as it is.
Honestly, I'm a little surprised by that; I thought ~650 would be a fairly safe guess for the combined strengths of the Clans. I thought estimates heading towards 700 would be a bit excessive, but it's starting to look like a fairly supportable guess.
With regard to Phelan's numbers, I'm given to understand that those figures include all warriors- so Watch agents and some WarShip and DropShip crew, along with all the fighters that operate out of carrier vessels.
*I also used 50 for the Star Adders, since IIRC the last time we went through their pre-Absorbtion numbers they had around that number- certainly in the higher forties; the Nova Cats got 40 since they were of similar size and power to other Clans with that number before their Abjuration.