Catalyzes both the N1-methylation of guanosine and the C7-methylation of 4-demethylwyosine (imG-14) at position 37 in tRNA(Phe). guanosine(37) in tRNA + S-adenosyl-L-methionine = H(+) + N(1)-methylguanosine(37) in tRNA + S-adenosyl-L-homocysteine 4-demethylwyosine(37) in tRNA(Phe) + S-adenosyl-L-methionine = H(+) + isowyosine(37) in tRNA(Phe) + S-adenosyl-L-homocysteine Less efficient than Trm5b and appears to be selective for methylating tRNA(Phe). Belongs to the class I-like SAM-binding methyltransferase superfamily. TRM5/TYW2 family.