Identify the product asked:

Salicylaldehyde is o-hydroxybenzaldehyde.

Recall the named reaction for preparing salicylaldehyde from phenol:

Phenol on treatment with chloroform and aqueous sodium hydroxide undergoes the Reimer–Tiemann reaction.

$\text{Phenol} \xrightarrow[\text{NaOH}]{\text{CHCl}_3} o\text{-hydroxybenzaldehyde}$

In this reaction, the formyl group $(-CHO)$ is introduced mainly at the ortho position of phenol, giving salicylaldehyde.

Check the options:

• A: $\mathrm{HCCl_3}, \mathrm{NaOH}$

  This is chloroform + sodium hydroxide, i.e. Reimer–Tiemann reaction. It gives salicylaldehyde. So correct.

• B: $\mathrm{CO_2}, \mathrm{NaOH}$

  This is related to the Kolbe–Schmitt reaction, which gives salicylic acid after acidification, not salicylaldehyde. So incorrect.

• D: $\mathrm{CCl_4}, \mathrm{NaOH}$

  With $\mathrm{CCl_4}$ and base, phenol gives salicylic acid (after hydrolysis), not salicylaldehyde. So incorrect.

Conclusion:

The reagent needed to synthesize salicylaldehyde from phenol is:

$\boxed{\mathrm{CHCl_3},\ \mathrm{NaOH}}$

Hence, Option A is correct.