In meiosis, what phase does the chromosomes synapse occur?

Meiosis tkes place in two steps: in each step nuclear materials divide. First division or Meiosis I is reductional division, second division or Meiosis II is equational division (like mitosis).

Meiosis I is subdivided as usual in
1. Prophase I
2. Metaphase I
3. Anaphase I
4. Telophase I

Prophase I is very elaborate phase. It is divided in Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis. In leptotene, chromosomes dehydrate and start to coil so that they appear as threads within nuceus.

Inside diploid cell, each chromosome is represented twice, i.e. in double dose and two such chromosomes are called homologous to each other. These homologous chromosomes tend to come together due to formation of a protein entity between them. Elements of the protein scaffolding or synaptonemal complex, as it is called, start to accumulate in leptotene.

In zygotene, the homologous chromosomes come together, lie side by side and the pairing is called synapsis .