The Accu-Scope EXC-360 Microscope is an excellent affordable microscope option for phase contrast applications.  This would be excellent for a water treatment plant or andrology/semen analysis laboratory 

Accu-Scope EXC-360 Microscope | Phase Contrast Microscope

Trinocular with Turret Phase Condenser & Plan Phase Objectives
Trinocular viewing head, inclined 30°, rotatable 360°; fixed light path split 50:50
PL10x/22mm focusable eyepieces with eye cushions; accepts 24mm reticle
Plan Phase 4x, 10x, 40xR, 100xR oil objectives
Double layer, rackless mechanical stage with ceramic insert, low position right hand controls
Turret phase contrast condenser with 10x, 20x, 40x and 100x phase annuli, BF position
Coaxial coarse and fine focus controls
3 watt Variable LED with field iris
5v USB charging port for personal mobile device
Dust cover, power cord, immersion oil and instruction manual