Why does aqueous sodium bicarbonate solution dissolve carboxylic acids but not phenol though they are also acidic ?

In both cases the product formed is carbonic acid (pKa=6) which is stronger acid than phenols (pKa=10) but weaker than carboxylic acid(pKa=4.5).

Acid-base equilibrium in second case shift more towards backward direction. Hence phenol does not react with NaHCO3.

Why enol form of Beta Dicarbonyl compound more stable than those of monocarbonyl compounds?

Enol form of Beta Dicarbonyl compounds are more stable because it has a conjugated π-system and intramolecular H-bonding.

Why enol form of phenol is more stable than its keto isomers?

Enol form of Phenol is more stable than keto form because it has a stable aromatic ring.