You don’t need a custom recovery to install /e/ on the Fairphone 3.
Also, the update mechanism of /e/ doesn’t rely on the recovery here (same as with the stock OS).
Furthermore, under normal circumstances you would not install a custom recovery on the Fairphone 3 anyway, you would just boot it when needed without installing it.
(The reason for this being … There is no separate recovery partition on the Fairphone 3 you could flash a custom recovery to. Installing a custom recovery on the Fairphone 3 means embedding it into the boot partition, so the boot partition gets altered. At least the stock OS updater checks for altered partitions and refuses to update in this case, though I don’t know how the /e/ updater handles that.)