diff --git a/components/autofill/core/browser/form_structure.cc b/components/autofill/core/browser/form_structure.cc
index a3f09721c3499..86d16c3a842b6 100644
--- a/components/autofill/core/browser/form_structure.cc
+++ b/components/autofill/core/browser/form_structure.cc
@@ -1596,7 +1596,7 @@ void FormStructure::RationalizeStreetAddressAndAddressLine(
 }
 
 void FormStructure::RationalizePhoneNumbersInSection(const Section& section) {
-  if (phone_rationalized_[section])
+  if (base::Contains(phone_rationalized_, section))
     return;
   std::vector<AutofillField*> fields;
   for (size_t i = 0; i < field_count(); ++i) {
@@ -1605,7 +1605,7 @@ void FormStructure::RationalizePhoneNumbersInSection(const Section& section) {
     fields.push_back(field(i));
   }
   rationalization_util::RationalizePhoneNumberFields(fields);
-  phone_rationalized_[section] = true;
+  phone_rationalized_.insert(section);
 }
 
 void FormStructure::ApplyRationalizationsToFieldAndLog(
diff --git a/components/autofill/core/browser/form_structure.h b/components/autofill/core/browser/form_structure.h
index f7e60834d7a7a..1c0859df4e698 100644
--- a/components/autofill/core/browser/form_structure.h
+++ b/components/autofill/core/browser/form_structure.h
@@ -7,7 +7,6 @@
 
 #include <stddef.h>
 
-#include <map>
 #include <memory>
 #include <set>
 #include <string>
@@ -669,7 +668,7 @@ class FormStructure {
   base::TimeTicks form_parsed_timestamp_;
 
   // If phone number rationalization has been performed for a given section.
-  std::map<Section, bool> phone_rationalized_;
+  std::set<Section> phone_rationalized_;
 
   // True iff the form is a password form and the user has seen the password
   // value before accepting the prompt to save. Used for crowdsourcing.
diff --git a/components/autofill/core/browser/form_structure_test_api.h b/components/autofill/core/browser/form_structure_test_api.h
index 940547d752d25..eeca25c1f6a6d 100644
--- a/components/autofill/core/browser/form_structure_test_api.h
+++ b/components/autofill/core/browser/form_structure_test_api.h
@@ -7,6 +7,7 @@
 
 #include <string>
 
+#include "base/containers/contains.h"
 #include "base/memory/raw_ptr.h"
 #include "base/strings/string_piece.h"
 #include "components/autofill/core/browser/form_structure.h"
@@ -67,8 +68,7 @@ class FormStructureTestApi {
   }
 
   bool phone_rationalized(const Section& section) const {
-    auto it = form_structure_->phone_rationalized_.find(section);
-    return it != form_structure_->phone_rationalized_.end() && it->second;
+    return base::Contains(form_structure_->phone_rationalized_, section);
   }
 
   void ParseFieldTypesWithPatterns(PatternSource pattern_source) {