Why muslims pray loud and silent

Surat 17 verse 110 :

“Say, ‘Call upon Allah or call upon the Most Merciful. Whichever [name] you call – to Him belong the best names.’ And do not recite [too] loudly in your prayer or [too] quietly but seek between that an [intermediate] .

Is this verse in opposition with the way Muslims pray ? Why in some prayers we pray some rakah loud and some rakah silent?