To compare the two fractions, we first express both of them in terms of a common denominator or compare their decimal equivalents directly.
The fraction Four-fifths is represented as: \[ \frac{4}{5} = \frac{16}{20} \]
Since both fractions are equal: \[ \frac{4}{5} = \frac{16}{20} \]
Therefore, the phrase that should be inserted is: is equal to.
So the completed statement is: Four-fifths is equal to StartFraction 16 Over 20 EndFraction.