Which of the following is most basic in nature?

Basicity of amines depends upon the availability of lone pair of nitrogen for donation. Electron releasing group like $-\mathrm{CH}_3$ increases the basicity of amines by increasing electron density over nitrogen, which facilitate the donation of lone pair of electrons. Electron withdrawing groups like -Ph group withdraws electrons and thus, make amines less basic by decreasing electron density over nitrogen. Hence, the order of basic nature of the given amines is $\left(\mathrm{CH}_3\right)_2 \mathrm{NH}\gt\mathrm{C}_6 \mathrm{H}_5 \mathrm{~N}\left(\mathrm{CH}_3\right)_2\gt\mathrm{CH}_3 \mathrm{NH}_2\gt\mathrm{NH}_3$ Thus, $\left(\mathrm{CH}_3\right)_2 \mathrm{NH}$ is most basic.