Iatrophobia - Fear of going to the doctor or of doctors.
Ichthyophobia - Fear of fish.
Ideophobia - Fear of ideas.
Illyngophobia - Fear of vertigo or feeling dizzy when looking down.
Iophobia - Fear of poison or rust. (Toxiphobia, Toxophobia, Toxicophobia)
Insectiphobia or Insectophobia - Fear of insects or bugs. (Entomophobia)
Isolophobia - Fear of solitude or being alone. (Autophobia, Monophobia, Eremiphobia, Eremiophobia, Eremophobia)
Isopterophobia - Fear of termites or insects that eat wood.
Ithyphallophobia - Fear of seeing, thinking about or having an erect penis. (Phallophobia, Medomalacophobia, Medomalacuphobia, Medorthophobia)