There have been some controversial speculations as to whether Galileo truly deserves the credit for these observations or it is actually his student Benedetto Castelli. This suspicion arises because of a letter written by Castelli to Galileo in December 1660 asking whether he could observe the phases of Venus using his new telescope, and there being no previous records of Galileo mentioning or discussing them. Also, in an encrypted letter to Johannes Kepler written mere days later, Galileo mentions his observations without any credit to Castelli.
The contents of the letter were –
Cynthiae figuras aemulatur mater amorum (The mother of love imitates the shape of Cynthia)
And he scrambled it as such –
Haec immatura a me iam frustra leguntur o.y. (These are now too young to be read by me)
The moon was popularly referred to as Cynthia in literary works and mother of love indicates Venus.