It appears that it is soluble but not absorbable in many animals but is by plants especially in water where it is broken down by biologic processes.

"Although it is unstable to heat, in geologically stable regions like Australia and Southern Africa, alumiunium phosphate is generally the most common form of phosphorus in soils, as it forms when phosphate in rainwater reacts with dissolved aluminium in the soil. Although it is not as insoluble as many other components of soils in those regions, aluminium phosphate can form exceedingly insoluble double salts known as taranakites with many essential elements for plant growth that are normally highly soluble in water, such as potassium and nitrogen."