It would be nice to see meaningful sentences among the exercises with these words (etapa, fasa etc.), not just "It is a stage" or "which phase?" kind of stuff because I can't figure out the exact meaning and supposed context of these words. I translate them literally but have no idea how these are used in "the real world".
Not a rule of Spanish grammar, but a common practice, linguistically, for vowels to slur together when one words ends in a vowel and the following words begins with a vowel. That is how "you all" becomes "y'all" Pretty much the way humans speak, unless they are paying careful attention, like radio broadcasters, etc.