1. A synergistic antimicrobial composition comprising: (a) a hydroxymethyl substituted phosphorus compound selected from the group consisting of tetrakis (hydroxymethyl) phosphonium and tris (hydroxymethyl) phosphine salts, and b) a second biocide selected from the group consisting of (1) hexahydro-1 , 3,5-tris (2-hydroxyethyl) -s-triazine, (2) 2,6-dimethyl-1,3-dioxan-4-yl acetate and (3) ortho-phenylphenol or its alkali metal or ammonium salts, the mass ratio of hydroxymethyl substituted phosphorus / hexahydro-1,3,5-tris (2-hydroxyethyl) -s-triazine is from 15: 1 about 1:15, the weight ratio of the hydroxymethyl substituted phosphorus / 2,6-dimethyl-1,3-dioxan-4-yl acetate is 15: 1 to 1:15, and the weight ratio of the hydroxymethyl substituted phosphorus / ortho-phenylphenol or alkali salts thereof metals or ammonium salts is from 15: 1 to 1: 5.2. The composition of claim 1, wherein the second biocide is hexahydro-1,3,5-tris (2-hydroxyethyl) -s-triazine. The composition according to claim 2, in which the mass ratio is from 12: 1 to 1: 12.4. The composition of claim 1, wherein the second biocide is 2,6-dimethyl-1,3-dioxan-4-yl acetate. The composition according to claim 4, in which the mass ratio is from 10: 1 to 1: 10.6. The composition of claim 1, wherein the second biocide is ortho-phenylphenol or an alkali metal salt or ammonium salt thereof. The method according to claim 6, where the mass ratio is from 10: 1 to 1: 4.1. Синергетическая противомикробная композиция, содержащая: (а) гидроксиметилзамещенное соединение фосфора, выбранное из группы, включающей соли тетракис(гидроксиметил)фосфония и трис(гидроксиметил)фосфин, и б) второй биоцид, выбранный из группы, включающей (1) гексагидро-1,3,5-трис(2-гидроксиэтил)-s-триазин, (2) 2,6-диметил-1,3-диоксан-4-илацетат и (3) орто-фенилфенол или его соли щелочных металлов или соли аммония, при этом массовое соотношение гидроксиметилзамещенное соединение фосфора/гексагидро-1,3,5-трис(2-гидроксиэтил)-s-триазин составляет от
