Upper critical solution temperatures (UCSTS ± 0.05 K) and mutual solubilities of phenol + water systems are reported separately with 0.5 millimol kg-1 (mm kg-1) proteins (casein, pepsin, egg-albumin), vitamins (B1-thiamine, B2-riboflavin, B6-pyridoxine), amino acids (glycine, β-alanine, L-leucine) and surfactants (dodecyl trimethylammonium bromide- DTAB, trimethylsulphoxonium iodide-TMSOI, methyltrioctylammonium chloride- MTOAC, orcinol). The additives decrease the UCSTs by about 0.50-2 0C with slight enhancement in mutual solubilities but the leucine with two –CH3 (methyl) and two - CH2- (methylene) groups produce negligible increase in the solubilities. The –CH3 and - CH2- groups develop stronger hydrophobic interactions but the glycine develops stronger hydrophilic interactions due to –N+H3 (amino) and –COO- (carboxylic) groups and weaker hydrophobic due to single –CH2- group. The leucine increases the solubility by 0.009 mole fractions with a 0.7 0C decrease in USCT as compared to phenol-water. The mole fractions of additives restricted to 0.002 to 0.005 range, the conjugations of casein and vitamins in place of –CH3 groups of amino acids enhance the solubility with lower UCST values.