Silicates and borates glasses, for example, there are several compositions which exhibit homogeneous bulk nucleation, however this does not occur aparentement for phosphates.
You can promote homogeneous nucleation by phase separation in a phosphate glass.. I suggest you to check out this article: Sycheva G.A. Transition from Heterogeneous to the Homogenous Nucleation in Some Silicate and Phosphate Glasses, Proceedings of the Internetional Symposum on Glass Problems, İstanbul, Turkey, September 4-6, 1996, vol.2 pp.373-379