Passavants ridge is formed by

Some of the upper fibres of the palatopharyngeus pass circularly deep to the mucous membrane of the pharynx and form a sphincter internal to the superior constrictor. These fibres constitute Passavant's muscle which on contraction raises a ridge called the Passavant's ridge on the posterior wall of the nasopharynx. When the soft palate is elevated it comes in contact with this ridge, the two together closing the pharyngeal isthmus between the nasopharynx and the oropharynx. Ref: BD Chaurasia's HUMAN ANATOMY, Volume 3, 4th edition.