After Screen replacement, cannot hear or talk on phone calls

Not sure why your loudspeaker would not be working, when doing a screen replacement. I would first try a soft reset by holding the home button and then power button until apple icon come on, see if the loud speaker or ear speaker are working. If not take phone apart, did you wear gloves during the repair if not clean the connectors with 91% alcohol because oil can cause problems, then make sure to clean the brass parts lightly on the speaker too, make sure the ear speaker is lined up correctly and test phone again.