In this set the spelling of /b/ is <b>, and the /ʒ/ sound is spelled <ge>.
The contrast is between a stop and a fricative, both voiced but well separated in the mouth. It is unlikely to be a problem.
The consonant /b/ can occur in any position in the syllable, but /ʒ/ only occurs finally or intervocalically, other than in foreign names. /ʒ/ is in any case a very rare phoneme, found in only 334 words in the source dictionary. The figure for the mean density of this contrast is 2/5372, too small to signify, while the semantic loading is 100%, since there are no pairs which are inflections of the same root.
babe beige rubies rouges
John Higgins, Shaftesbury, January 2010.