How is the divinity of Jesus defended in light of Philippians 2:9 ("God exalted him") and Matthew 28:18? Philippians 2:9
  Therefore God exalted him to the highest place and gave him the name that is above every name
  
  Matthew 28:18
  Then Jesus came to them and said, "All authority in heaven and on earth has been given to me."


In the first of the verses mentioned above, Scripture talks about God exalted Jesus, and the second verse talks about Jesus gaining all authority on heaven and on Earth. If Jesus is God, why would he need to be exalted and given authority, especially considering that exaltation and authority are qualities already possessed by God?
Paul says of the Son of God, that 'being in the form of God, he thought it not robbery to be equal with God'[Philippians 2:6 KJV] . He is equal to God, in his eternal Being.

The two texts you mention regard the Son of God being exalted in humanity. That is, after incarnation and after his sufferings and death, God exalted Jesus Christ to his own right hand - in humanity.

The first humanity failed. For all have sinned and come short of the glory of God, Romans 3:23. 

But Jesus Christ, in humanity, did - always - the will of the Father, John 8:29. Thus has God exalted him, in humanity, to his own throne, Revelation 3:21.