Philip Larkin is generally acknowledged to be a poet of The Movement, which grew up out of and was a reaction against the Modernist movement. Each has distinguishing characteristics that are opposed to each other and Larkin's work fits firmly in the characteristics that define The Movement. These characteristics pertain to form, self, individualism, and realism.
Modernism rejected conventional poetic form and presented itself as a fragmentation of form, which was visible in experimentation with genre and the fragmentation of time, which presented events in a non-chronological, non-linear, non-unified order. Self, the ontological representation of the speaker and/or writer, is alienated--from self and society--and similarly fragmented. Characterization or defining qualities are obscure and possibly shallow, making knowledge of the presented self elusive.
In Modernist poetry, individualism is a paramount concern. In this sense, individualism refers to representing the speaker's and/or writer's personal, individual experience regardless of whether it may or may not represent a universal commonality amongst people. A correlated characteristic is the representation of a Modernist world view that is anti-realism, meaning Modernist poems are not meant nor desired to be held up to reality as a true representation or a reliable mirror of life or the world.
On the other hand, the poets of The Movement embraced a return to form as a reaction against the fragmentation of form begun by the Modernists. Regarding self, The Movement offered straightforward representations of the self of the poetic speaker or writer, and, in that sense, presented a positive ontological view of self as opposed to the Modernist alienated ontological view. In correlation with self, the individualism of Modernism gave way to The Movement's representation of the individual in relation to society, reacting to, and often reacting against, society.
While Modernists embraced experimentation of form, The Movement embraced the forms and conventions of previously established poetic genres, embracing structure in reaction against the Modernist's abandonment of structure. In addition, while Modernists adhered to anti-realism, The Movement reflected the reality of the mundane commonplace that was more realistic than the realism begun in the Romantic period. Whereas Wordsworth, the founder of English poetic Romanticism, laced his realism with metaphor and what might be called low poetic diction, The Movement eschewed literary devices, striving for plain, direct language devoid of simile, metaphor, symbolism or other literary techniques.
Larkin's poetry displays all these characteristics, from the structure of his composition to the straightforward ontological representation of self devoid of alienation to the individual experience in society (not eccentrically isolated) to the form and conventions of poetry that couched the descriptions of the unembellished commonplaces of life. Philip Larkin is in fact a true representative of The Movement because his poems both adhere to and help define the definitive characteristics of The Movement.
[For further information, see the links to TextEtc.com and EdSitement, National Endowment for the Arts from which this answer is drawn.]