Kenneth Mallor, the young pianist who played at the Phillips Collection yesterday, is traveling a familiar path. It leads through Eastman and Juilliard, with excursions to competitions here and abroad. On the way he has acquired a respectable technique and, one assumes, a good-sized repertoire.

Certainly the music Mallor chose for yesterday's program was from among the big guns of piano literature; the Beethoven Sonat Op 110, prokofiev's Sonata in B Flat, No. 7, and the Chopin B Flat Minor Sonata Op. 35.

In short, he has become a pianist, but he is not yet an artist.

At the moment his concentration seems to be on large phrases in the music, on the bridge section of the Beethoven fugue, on the events in the Prokofiev first movement. The shapes of these phrases are well-contoured, but along the way both the small and the large picture are given short shrift. The details are slighted and the movements themselves lack coherence.

This was nowhere more evident than in the first two movements of the Beethoven, where sloppy fingerwork marred the counterpoint and lack of balance, the structure.

That Mallor put everything together so well for the last movement of the Prokofiev, however, indicates that he is still traveling, and in the right direction.