If your phone has a USB charge port- as most do- the voltage will be standard, at 5 volts. By default all USB chargers will provide this amount of voltage. If it's got the capability, when you connect it the phone may be able to use higher voltages, like 9 or 20 volts.

Your phone may want more power than a basic charger can deliver, in which case it'll charge slowly- and in some cases, such as a cheap or old charger, may overload the charger causing it to heat up or fail- usually by burning a component.

A higher-power charger may allow your phone to charge with higher current levels (more power), and charge more quickly. This would only apply to USB-C type chargers, the ones that are reversible. Older chargers are more limited in power delivery.

If your phone doesn't use a USB port for connecting a charge cable, you must use a charger with the correct voltage and current for it. I'm not familiar with any modern phone that does this, though.