If the Sun were at the vernal equinox ( March 20-21) and the Moon were there too, the phase would be New Moon because the Sun would be directly behind the Moon. Also, if they were coincident, there would be a total solar eclipse. I looked at the "Canon of Eclipses" by Th. Oppolzer, translated and reprinted in 1961 by Owen Gingerich with Dover Publishing, and had a look at the last time there was a total eclipse of the Sun on or near the date of the vernal equinox. On March 21, 1765 ( eclipse number 7075) such a thing did occur. There have also been several solar eclipses since then within a few days of the vernal equinox on March 18, 1988, March 18, 1969, March 24, 1811 and March 22, 1792. The next solar eclipse will occur near the vernal equinox on March 19, 2007 and March 20, 2015.
If the Sun were at the vernal equinox, and the Moon were located at the summer solstice position, you would have a First Quarter Moon. The last time this happened was on March 20, 1994.