Although Phenidone is broadly used as a 'substitute' for Metol, the detailed constituents of equivalent formulae are quite different.(posted 8572 days ago)
For instance; ID68 (Phenidone) was formulated to give very similar results to D76 (Metol), but the Phenidone formula is nowhere near the same as the Metol version.
Simply replacing Phenidone with Metol will almost certainly work as a developer, but won't give the same result, and won't have the same development time.As I see it, there are two ways round this.
1)If the problem is simply one of weighing out, then you can weigh a larger quantity of Phenidone powder, arrange it into a neat shape and simply divide it into 2 or 4, or make up a stock solution of, say, 10 gm in 100ml of distilled water, with 20gm of Sodium Sulphite to preserve it. Then if the formula calls for 0.75 gm, just use a syringe to measure 7.5ml of the solution.
2)Alternatively, use a published Metol formula which is the functional equivalent of the Phenidone one.
The later editions of Jacob's 'Developing', Focal press; gives a whole range of modern(ish) formulae to cover practically every need, and I have a fairly comprehensive library of formulary myself. If you tell me the Phenidone formula, I can most likely find the Metol equivalent for you.