Michelle is holding a boiling tube containing colourless limewater Ca(OH)₂ - aqueous calcium hydroxide.

She then added colourless phenolphthalein which turned pink in aqueous calcium hydroxide.

The hydroxyl (OH)^- ions present in limewater is the cause of  colourless phenolphthalein turning pink. This shows that the pH value to be greater than 9.

After blowing into the test tube vigorously for about 2 minutes or so, the pink colour of the phenolphthalein slowly turned less pink.

Reason: As more and more calcium carbonate precipitate is formed, less and less hydroxyl (OH)^- ions remained in the solution, accounting for the lighter pink colouration.

...finally the pink phenolphthalein turned colourless.

The pink coloration will disappear when all the aqueous calcium hydroxide is used up (to form the white precipitate of calcium carbonate and water) leaving no more (OH)^- ions in the solution.

Ca(OH)_2(aq)   + CO_2(g)  → CaCO_3(s) + H₂O _(l)

The hydroxyl ions are actually extracted to form water.