I have looked in the styles menu under Frame and Graphic but I do not see this option anywhere.
A popular topic since OOo 1.1
→ OOo Bug 14008 - Allow anchor settings in frame styles (graphic-styles) [2003-05-02]
→ OOo Bug 19814 - default anchor type: toolbar icon to select anchor type of newly to be inserted objects [2003-09-19]
→ Bug 32484 - Allow anchor settings in frame styles [2010-12-17]
→ Bug 36535 - Formatting and stylist frame [2011-04-23]
→ Unable to save Anchor as Character as default style Build 3.5.42 [LibreOffice Users, 2012-07-03]
→ image anchoring [LibreOffice Users, 2012-10-21]
Presetting the anchorage - as of version 7.1
The anchoring for inserting images can be preset from LibreOffice version 7.1.
Select Tools>Options>LibreOffice Writer>Formatting Aids from the menu.
For Image/Anchor you can select: To Pragraph, To Character or As Character.