To draw a Lewis structure, it is not necessary to know The length of the bonds.
The types of atoms in the molecule.
The number of valence electrons for each atom.
The number of atoms in the molecule.

This answer to this question is the. Type of atoms in the molecule

The moles have to be equal. Always start with a balanced equation. This reaction is a double replacement.
The basic equation is
NaOH + H3PO4 ===> Na3PO4 + HOH

The balanced equation is.
3NaOH + H3PO4 ===> Na3PO4 + 3HOH

moles of NaOH = moles of H3PO4
mols of NaOH = molarity * Volume
molarity = 0.35 mol/L
Volume = 1.0 L
moles NaOH = 0.35 * 1 = 0.35 mols

Find the moles of H3PO4
For every mol of H3PO4 used, you require 3 mols of NaOH
3/1 = 0.35/x
3x = 0.35
x = 0.35/3
x = 0.1167 moles of H3PO4 needed for this reaction.

Now the volume needs to be calculated.
n = 0.1167
M = 0.25 mol/L
V = ??

Formula
M = n/V
V = n/M
V = 0.1157/0.25 
V = 0.467 L

Note: I merely copied the reaction given myself to the next line. I'm not copying from an outside source.