Answer:
With increase in pH i.e. making solvents basic - you will get increase RT for most compounds and reduced peak tailing.
With decrease in pH i.e. making solvents acidid - you will get decrease RT for most compounds.
However this WONT be true for all columns. You cannot use random column at pH 1.5 - this will damage your column and same applies to working at high pHs - i.e. working at pH 13 - will damage most columns.
Always check the pH capacity in HPLC before choosing mobile phase pHs
Source: I am analytical scientist.