Please try to adjust Jitter Buffer duration on Talkatone/Call Settings. This controls internal audio buffer duration.
The problem with Android devices is that their hardware + OS-level audio buffers are just enormously large and it causes significant lag during conversation.
So we can reduce our application-level buffers to reduce the lag. The problem here is that when we reduce application layer buffer we tolerate less of network problems (e.g. when audio packets delayed longer than duration of jitter buffer we start treating them as "lost").
Recommended value: "Normal".
On good wifi connections users may get better result by reducing it to "short" (half of normal).
On excellent - to "Aggressive".
On 3G/4G it is NOT recommended to reduce it from Normal.
See Video Tutorial