My charger is lost so I am using a charger with an output of 5.5v and 0.6A. My real charger gives an output of 5V and 0.7A. Will the other charger damage my phone?
No, it will not damage your phone. As long as it's a micro USB charger, it will be fine.
5.5V is fine, I've had success with 6 Volts from a homemade charger, and you won't meet voltages higher than 5.5V on a micro USB charger anyway. Extra Volts are dangerous, so it's good to be cautious but 5.5V will not do any harm.
The current rating (Amperes, A) does not count; if it's too low, the phone may charge slowly or not at all, but higher rated chargers will not do harm.