This section is a fughetta (or, in fugato style):
a short fugue, with exposition plus only a few restatements of the subject. Fugato applies to music where only part of a fugue — usually an exposition — appears in a context that is not otherwise fugal, as a means of thematic development. (Source: Brittanica)
Serrano-Ayala et al. (2018) provide a detailed analysis, including the below reference:1
The structural breakdown according to Glazunov himself, taken from a letter he wrote to Maximilian Steinberg:
• Exposition: Allegro Moderato, in 4/4, ending in G minor
• Development (brief)
• Transition: Andante (C flat major; sometimes B major), in 3/4, leading into a small cadenza
• Conclusion: Fugato (C minor), in 12/8
The above forms occur again before leading to the coda (E flat major).
Their article includes the following commentary on this section of the piece (143):
Conclusion. Fugato. (C minor), in 12/8. The famous fughetta (because for many years it was imagined that Glazunov left off work here) explodes the initial statement so that the composer has people thinking they are in for some kind of enormous fugal episode. But his real motive is to familiarize them with the insistent triplet-loaded twelve/eight meter that he will ingeniously use to pit twos against threes in a very Brahmsian topsy-turvy rhythm.
Glazunov again imitates the first movement’s A-a B-b structure, each theme being a variant on its corresponding theme in the first section, moving into an extended coda that recapitulates many of the motives in a shifting cornucopia of melodic invention.
1 Sebastian Ariel Serrano-Ayala, Nerilyn Ann Beratio,
Khristine Ruth De Gracia, Sherryl Ann de Dios, Aera Jean Apalat, "Concerto in E Flat Major for Alto Saxophone and String Orchestra Opus 109 by Alexander Glazunov: A Structural Analysis for Teaching Intermediate Level", Journal of Education, Psychology, and Humanities 1/1 (2018). The quoted material (emphasis mine) appears on page 140, which also includes a complete outline of the piece's form. The source letter to "M. Steinberg" is originally cited in André Sobchenko, "Letters From Glazunov
'The Saxophone Concerto Years'", Saxophone Journal, 66–70 (here, page 68): Sept/Oct. 1997.