Going off the definition of a Lich given from Wikipedia:
A lich is a type of undead creature. Often such a creature is the result of a transformation, as a powerful magician or king striving for eternal life uses spells or rituals to bind his intellect and soul to his phylactery and thereby achieve a form of immortality. Liches are depicted as being clearly cadaverous, bodies desiccated or completely skeletal. Liches are often depicted as holding power over hordes of lesser undead creatures, using them as soldiers and servants. Unlike zombies, which are often depicted as mindless, a lich retains independent thought and is usually at least as intelligent as it was prior to its transformation. -Wikipedia
Voldemort is known to be an extremely powerful wizard who has utilized dark magic to unnaturally prolong his life, even going as far as trying to attain immortality though the creation of Horcruxes. Voldemort has accomplished this by binding parts of his will and soul to the various Horcruxes, very similar to how a lich utilizes a phylactery.
While Voldemort isn't depicted as being skeletal, his body has been transformed by his resurrection and does appear very ghoulish.
Voldemort does appear to hold unnatural power over hordes of lesser beings.
Looking further into the article on Wikipedia there is a small section that states:
In the Harry Potter book series, the primary antagonist Voldemort is a dark wizard who separates his soul from his body using magic, and then imbues these soul fragments into various objects, creatures, and people. He is thereafter unable to be killed until said vessels are destroyed, making him and his Horcruxes very similar to the concept of a lich and its phylactery. -Wikipedia
However, there are no sources cited to verify this.
Has J.K. Rowling made any indication that Voldemort is in fact a lich?