\draw (-2.25,0) node[left] {$\varphi_a$} -- (2.25,0) node[right] {$\varphi_b$}; \draw[->,yshift=5pt] (-2,0) -- (-1,0) node[midway,above] {$p_1$}; \draw[->,yshift=5pt ...

\draw (-2,0) node[left] {$\varphi_a$} -- (2,0) node[right] {$\varphi_c$} (0,2) node[above] {$\varphi_b$} -- (0,-2) node[below] {$\varphi_d$}; \draw[->,yshift=5pt] (-1 ...