This Trophy is for looking at a girly poster while calling Otacon on the Codec. The first opportunity to do this is right at the beginning of the Tanker chapter. Enter the interior of the ship through either the right or left door. Now head to the locker area.
Open the top left locker. There should be a poster of a girl in a bikini. Enter first person view mode with the R button, then press Select to open the Codec. Call Otacon on the regular frequency (141.12, not the save frequency), and he should make a remark about the situation. Snake's face should also appear to be...distracted.