The Leo would need a warrant to see the cellphone. They cannot take it.
This is incorrect. LEO can take cell phones pursuant to an arrest if the cell phone is part of the criminality:
1. Any controlled substance as defined in chapter 893 or any substance, device, paraphernalia, or currency or other means of exchange that was used, was attempted to be used, or was intended to be used in violation of any provision of chapter 893, if the totality of the facts presented by the state is clearly sufficient to meet the state’s burden of establishing probable cause to believe that a nexus exists between the article seized and the narcotics activity, whether or not the use of the contraband article can be traced to a specific narcotics transaction.
They cannot under recent Florida Supreme Court decisions look at the content of the phone without a warrant, which will only issue pursuant to probable cause that the content on that phone can be tied to a criminal act, however they can depending on the circumstances take possession of the phone.
Now in some states if the person driving is charged with a DUI, the vehicle and its contents may be subject to civil forfeiture. Typically, a cell phone would be released in a DUI , but in a drug related forfeiture probably not. Texting while driving where the officer believes the texting was part of the scope of the criminal actions would certainly require the warrant where recently in 2013 the Florida Suprmes struck down where police officers looked at the phone content of suspected robbers and saw that they had taken pictures of the robbed loot and them holding the money.
So to give a general statement that they cannot take possession of a phone in incorrect, but once they have possession the Florida Supreme Court wants to see a warrant before the content of that device is disclosed.