A point marker symbol can overlap other symbols in the ArcMap Table of Contents (TOC) if the symbol has a relatively large Y-offset.
The TOC adjusts the vertical space required for each entry based on a symbol's size; extra space is created for larger symbols. However, the TOC does not provide extra vertical space to account for symbol offset.
Consequently, if one or more symbols in the TOC have Y-offsets, they may overlap other symbols.
A. Press the '+' button to create a maker symbol on a new level.
B. Pick No Color for the marker symbol
C. Increase the size of the symbol