S-adenosyl-L-methionine-dependent methyltransferase that catalyzes the methylation of the guanosine nucleotide at position 6 (m2G6) in tRNA(Phe). guanosine(6) in tRNA + S-adenosyl-L-methionine = H(+) + N(2)-methylguanosine(6) in tRNA + S-adenosyl-L-homocysteine Monomer in solution. Consists of an N-terminal THUMP domain fused to a catalytic Rossmann-fold MTase (RFM) domain. Inactivation of the gene leads to a total absence of m(2)G in tRNA but does not affect cell growth or the formation of other modified nucleosides in tRNA(Phe). Belongs to the methyltransferase superfamily.