N-methylethanolamine phosphate + S-adenosyl-L-methionine = N,N-dimethylethanolamine phosphate + S-adenosyl-L-homocysteine + H(+)
n-methylethanolamine phosphate + s-adenosyl-l-methionine = n,n-dimethylethanolamine phosphate + s-adenosyl-l-homocysteine + h(+)