Triphylite
Searching for other iron (II) phosphate minerals I found triphylite. It is a lithium iron (II) phosphate mineral with the chemical formula LiFe2+PO4. It’s named in 1834 by Johann Nepomunk von Fuchs after Greek words “tria” and “phylon” which means the “family of threesome” referring to the three cations of this mineral - lithium, iron and... manganese. Triphylite occurs together with lithiophilite (lithium manganese phosphate LiMnPO4) and forms solid solutions with it. That explains the presence of manganese in triphylite. Magnesium is another element that is often found in this mineral in minor quantities.
Weathering in the presence of water results in iron (II) oxidation to iron (III) and the formation of siderite (iron (III) carbonate) and phosphosiderite (iron (III) phosphate) among others.
First found in Germany, Zwiesel. But also occurs in Mangualde, Portugal and Samjon village, Tajikistan.
An example of triphylite from the mineraloftheday-blog.tumblr.com tumblr:
Some more pictures and information:
Mineralienatlas - Fossilienatlas
Mindat.org
Another mineral graftonite, an iron (II), manganese and calcium phosphate with the formula (Fe2+,Mn,Ca)3(PO4)2.
More information:
Wikipedia
Mindat.org