Are pKa values of acid and conjugate base the same? When you look at $\mathrm{p}K_\mathrm{a}$ table, you can read $\mathrm{p}K_\mathrm{a}$ values of acids. Do conjugate bases also have $\mathrm{p}K_\mathrm{a}$ values?

If both can have $\mathrm{p}K_\mathrm{a}$ values, why $\mathrm{p}K_\mathrm{a}$ value of conjugated bases are same as acids?
Can acid have only $\mathrm{p}K_\mathrm{a}$ values, not $\mathrm{p}K_\mathrm{b}$ values?
Let consider the case of the phosphoric acid.

The phosphoric acid $\ce{H3PO4}$ has $pK_\mathrm{a1}$.
Its conjugate base $\ce{H2PO4-}$ has $pK_\mathrm{b1} = 14- pK_\mathrm{a1}$.

But as $\ce{H2PO4-}$  is at the same time a ( weaker ) acid as well,
it has its own acidity constant $pK_\mathrm{a2}$ independent  on $pK_\mathrm{a1}$ and $pK_\mathrm{b1}$.

Generally, acids like $\ce{HA-}$ have $pK_\mathrm{a2}$ and $pK_\mathrm{b1}$ values.
The former associated with $\ce{HA- &lt;=&gt; H+ + A^2-}$,
the latter associated with $\ce{HA- + H2O &lt;=&gt; H2A + OH-}$