Analytical Chemistry predicting the order of elution of compounds in a reverse phase HPLC

Predict the order of elution for a mixture containing caffeine and benzoic acid, using a reverse phase HPLC. Explain your answer.

My try

Since benzoic acid is more acidic that caffeine, which means it has a lower PH, it is hence more polar. Since for HPLC, the mobile phase is the polar phase, elution of polar compounds will be favoured hence benzonic acid will be eluted first. Is my answer and explanation correct. Could anyone explain. Thanks

The logic is wrong. Lower $pH$ (actually you mean $pK_{a}$ here) does not mean more polar.