Its possible to obtain your product by first halogenation ArCH3 group with Cl2 to mono or dichloro aducts but as having OH phenolic group then its possible such reaction to lead also to Ar-halogenation...If not so then:
Ar-CH3 + Cl2 --> Ar-CH2Cl (as o-hidroxy benzyl chloride
The using Sommelet reaction with hexamethylenetetramine (urotropin) at heating which should lead to salycilic aldehyde:
Ar-CH2Cl + C6H12N4 + H2O -->Ar-CHO
Y
then you may easili oxidize salycilic aldehyde to salycilic acid with some weak oxidizing agent or with air and some salt catalyst..
From dihalo product:
Ar-CHCl2 + NaOH/H2O --> ArCHO and so on...
Of course classic Colbe method starting simply from Na-phenolate and CO2 to salycilic acid is most practically efficient i think.