I would like to know if I can change the phoneHomeIntervalInSecs time in sec dynamically or do i need to do a restart.
When the phoneHomeIntervalInSecs is changed, you must restart the forwarder. That is usually not a problem on a forwarder.
However, it could be a problem on an indexer or search head. I don't know if this will work but you could try
or the equivalent REST endpoint. I know this causes Splunk to rescan props.conf and transforms.conf, but I don't know if it will pick up deploymentclient.conf