Yesod represents the principle of connection, often someone or something standing at a junction between two points. This is the place of the tzadik who chooses to serve G-d, often over the pleasures of the world.
Joseph is seen in this role, particularly in his refusal of the temptation of Potiphar’s wife, who then falsely accused him. Sexuality has an important role regarding Yesod. G-d’s instructions regarding such matters reflect higher spiritual principles.
Joseph is also seen as establishing the divine connection between G-d and his brothers, who were made aware by him that even their own ‘evil’ actions were all part of “Hashgaha Pratit” – Specific Divine Providence.
“When you have purified your mind, there is no difference between this world, the grave, and the next world. When you only desire G-d and His Torah, all are the same. In all three you can be attached to God and his Torah. However, if you are attached to this world, there is an agonizing difference. This world is spread before you while the grave is tight and narrow. But when you purify your mind, all will be the same.” – Rabbi Nachman, Sichot Haran #51
A woman in the Torah fulfilling this role is Tamar, who not only ‘connected’ with Judah physically, but made the Torah connection which resulted in her being part of the lineage of the messiah.