The recommendation is to use letters of the Greek Alphabet, i.e., Alpha, Beta, Gamma to label the variants. As such, Variant of Interest (VOI) P.3 which was first detected in the Philippines (Jan-21)1 is now labeled by WHO as Theta.
PGC SARS-CoV-2 Bulletin No. 7: Detection and characterization of a new SARS-CoV-2 lineage P.3, with spike protein mutations E484K, N501Y, P681H and LGV 141-143 deletion, from samples sequenced through the intensified UP-PGC, UP-NIH and DOH biosurveillance program
A close examination of the mutation profile of the P.3 viruses revealed that apart from E484K and N501Y, they also share other spike protein mutations that are likely to have functional significance (Figure 2). This includes the P681H mutation, also found in lineage B.1.1.7 viruses, as well as a three-amino acid deletion at positions 141 to 143 (LGV141_143del).