I’m trying to pass values between textbox in template/report/grid.phtml and Mage_Adminhtml_Block_Report_Grid I know how to view values in .phtml file but how I get the values entered by user from phtml widget and use it in Mage_Adminhtml_Block_Report_Grid
It's impossible in that way, as you described it.
For example when user enter something in form on *.phtml page, usually you submit him to some Controller Action. Then you reload a page and deliver user to other (or same) page.
If you want deliver him to same page and pass new parameters to your Block, read this answer, its quite good explaining that