I’m sorry to hear that you are having trouble with purifying the phi29 DNA polymerase. Several factors could affect the protein activity and purity, such as the expression system, the purification method, the storage conditions, and the activity assay. Here are some suggestions that might help you:

• You could use E. coli cells with a cloned gene 2 of Bacillus subtilis phage phi291, the commercial phi29 DNA polymerase source for the expression system. This might ensure a high yield and quality of the enzyme.
• For the purification method, you could combine host DNA removal using appropriate salt concentrations, inactivation of amplifiable DNA using ethidium monoazide, and irradiation with visible light from a light-emitting diode lamp. This might reduce the nucleic acid contamination and improve the purity of the enzyme.
• For the storage conditions, you should store the enzyme at -20°C in a buffer containing 50 mM Tris-HCl (pH 7.5), 0.1 mM EDTA, 1 mM DTT, 100 mM KCl, 0.5% (v/v) Nonidet P40, 0.5% (v/v) Tween 20 and 50% (v/v) glycerol. This might prevent the enzyme from losing activity or degrading over time.
• For the activity assay, try using a fluorometric assay kit that measures the incorporation of dNTPs into a double-stranded DNA product that binds to a fluorescent dye. This might provide an easy and accurate way to determine the enzyme's activity without radioisotopes.