I don't see an attached picture, but I think I understand what you are trying to do.
First, I recommend trying tiledlayout instead of subplot, but both can handle what you are trying to do. tiledlayout and nexttile are newer than subplot and provide a few new features that should make this tast easier.
Conceptually, what you want is a grid that is 6 rows and 3 columns, then you want tiles in the grid to be either 2 or 3 rows tall.
t = tiledlayout(6,3);
ax11 = nexttile(1,[2 1]); % First column, top two rows
ax21 = nexttile(2,[2 1]); % Second column, top two rows
ax31 = nexttile(3,[3 1]); % Third column, top three rows
ax12 = nexttile(7,[2 1]); % First column, next two rows
ax22 = nexttile(8,[2 1]); % Second column, next two rows
ax32 = nexttile(12,[3 1]); % Third column, bottom three rows
ax13 = nexttile(13,[2 1]); % First column, bottom two rows
ax23 = nexttile(14,[2 1]); % Second column, bottom two rows
figure
ax11 = subplot(6,3,[1 4]); % First column, top two rows
ax21 = subplot(6,3,[2 5]); % Second column, top two rows
ax31 = subplot(6,3,[3 6 9]); % Third column, top three rows
ax12 = subplot(6,3,[7 10]); % First column, next two rows
ax22 = subplot(6,3,[8 11]); % Second column, next two rows
ax32 = subplot(6,3,[12 15 18]); % Third column, bottom three rows
ax13 = subplot(6,3,[13 16]); % First column, bottom two rows
ax23 = subplot(6,3,[14 17]); % Second column, bottom two rows
