Others leave this point blank or place a dash wherever this occurs. Some authors print only the upper one-half of a correlation matrix, since the lower half is the mirror image and thus, redundant. Notation is r, with pb subscript. Biserial is used when one variable is continuous and another is usually continuous, but which is forced into a dichotomy. This dichotomy is artificial.
Notation is r with b subscript.
Phi is when each of the varibles are naturally occuring, dichtomies. Ex. - gender with handedness. Notation is a circle with a line through it vertically. Tetrachoric correlation is two artificially dichotomous variables.