Whether a solvent is non-polar or polar is not an either/or sittuation. There is a continuous scale of polarity. Isopropanol can be considered a polar solvent. The hydroxide group creates enough of a dipole for it to interact with many polar groups, and the hydroxide also enables it to hydrogen bond to (making is a protic solvent as well). However, the hydrocarbon chain gives it some qualities of a non-polar solvent as well. Therefore, isopropanol is still a polar solvent, but it is considerably less polar than water. Isopropanol can still disolve water (probably because of its ability to hydrogen bond), but since it has some non-polar characteristics, it can disolve some organic compounds that are insoluble in water -- for example, membrane phospholipids (in the OP's example) or pen ink. Similarly, since it is less polar than water, isopropanol cannot disolve some highly polar/ionic compounds that are soluble in water, such as NaCl.