Bishops are sacramentally
equal, but may function differently in church administration.
First, there are Diocesan Bishops. These are bishops that rule a diocese in their own right. No bishops may serve in their diocese without their blessing (this includes if a metropolitan/patriarch wants to serve in a diocesan bishop's territory). For example, the Patriarch Kyril of Moscow may come to the US, but he cannot serve until Metropolitan Hilarion (First Hierarch of ROCOR) gives his blessing.
Then, there are Auxilary Bishops. These are bishops with a see, but not ruling over their own diocese. Usually, they will have a see next to a ruling bishop's see. A recent example is how Bishop Mark, formerly of the Antiochians and now in the OCA, is currently Bishop of Baltimore, serving as an auxillary to Metropolitan Jonah, because Vladyka Jonah's see is Washington, D.C. and Baltimore is close by. Auxilary Bishops work administratively under their Diocesan Bishop, essentially doing what he asks of them, but they are still sacramentally bishops. They may ordain clergy, serve heirarchial liturgies, etc. They ARE bishops, and act as them. They simply do not have their own diocese.
Yet, all bishops sit upon the Great Synod of an autocephelous church and have a vote. The first heirarch (read, primate) of an autocelphelous church is the first among equals in his church, but he is among equals, and may be outvoted at a meeting of the Synod, and even removed from office by the Holy Synod (as mentioned earlier).
Above this, even, exists the Diptychs of the Holy Orthodox Church, which are read when a service is held by a primatial bishop. In normal services, we commemorate our bishop, archbishop/metropolitan and patriarch. But, when a primatial bishop is serving, he commemorates the heads of the other autocelphelous churches, in honor by rank. This begins with the Ecumenical Patriarch, who is first among equals for all Orthodox bishops, and lists, in order of precedence, each Orthodox primate.
In short, all bishops are equal. Some are just more equal than others.